Ondular washer or wave-shaped spring with a defined progressive characteristic spring rate

ABSTRACT

An axially acting ondular washer or wave-shaped spring consisting of a closed annular member which comprises a central X-axis and which is periodically wave-shaped across the circumference, wherein a wave line extends so as to monotonically rise or fall between a plurality of identical minima and identical maxima and wherein in the minima and maximum of the wave line there are formed contact points of the annular member relative to axis-normal contact faces, wherein, starting from each minimum and maximum, the annular member, on both sides, i.e. in each circumferential direction, comprises at least two wave line portions which directly adjoin one another and which, with an increasing axial load, are individually flattened and made to contact and contact faces one after the other.

DESCRIPTION

The invention relates to an axially acting ondular washer or wave-shaped spring consisting of a closed annular member which comprises a central X-axis and which is periodically ondulated across the circumference, wherein a wave line extends between a plurality of identical minima and identical maxima and wherein at the unloaded annular member in the minima and maxima of the wave line there are formed contact points of the annular member relative to axis-normal contact faces and between the contact points there extend contact-free wave line ranges. Such ondular washer or wave-shaped spring according to the state of the art comprise a linear or continuously progressive characteristic spring rate which is predetermined by an approximately sinusoidal extension of the wave line if viewed across the circumference. Such a linear or continuously progressive spring rate is unsuitable for certain applications. Also, the spring rate of such wave-shaped springs in absolute terms is inadequate for some applications.

From the applicant's earlier non-published German patent application 103 21.800.9, there is known an ondular washer or wave-shaped spring whose characteristic spring rate progresses stepwise. However, across its circumference, said spring comprises a wave line extension with absolute and relative minima and maxima of different magnitudes and thus refers to a different type.

It is therefore the object of the present invention to provide an ondular washer or wave-shaped spring of the initially mentioned type having a characteristic spring curve which increases stepwise.

The objective is achieved in that, starting from each minimum and maximum, the annular member, on both sides, i.e. in each circumferential direction, comprises at least two wave line portions which directly adjoin one another and which, with an increasing axial load on the annular member, are individually flattened and are made to contact the contact faces one after the other.

More particularly, it is proposed that, with an increasing axial load, the contact points of the annular member relative to the contact faces lying at the ends of the contact-free wave line ranges, discontinuously, i.e. stepwise, move away from the original minima and maxima.

Furthermore, the objective is achieved in that, starting from each minimum and maximum, the annular member, on both sides, i.e. in each circumferential direction, comprises at least two wave line portions which directly adjoin one another and which correspond to the curved lines of bending beams loaded at their free ends by an individual load, wherein the curved lines of the individual wave line portions are based on individual loads which increase with an increasing distance from the original minima and maxima.

This means that the single wave line portions are designed like the curved lines of bending beams, clamped in at their one end and loaded by an individual load at their other free end. At calculation of these curved lines defining the wave line portions there is assumed a fictive individual load increasing respectively from one wave line portion to the next one. When loading the annular member in reality with a corresponding individual load at one of the contact points hence the adjoining wave line portion is deformed to a straight line, so that the respective wave line portion as a whole flatly contacts one of the contact faces.

Alternatively the objective is achieved in that the annular member is so designed that at compression in direction of the X-axis under an increasing axial load there are provided at least two adjoining ranges of travel h₁, h₂, the spring rates r₁, r₂ of which are each constant, but increasing from one to the next with an increasing path of travel (r₂>r₁).

Furthermore the objective is achieved in that, starting from each minimum and maximum, the annular member, in each circumferential direction comprises at least two wave line portions φ₁, φ₂ which directly adjoin one another and which each have a constant gradient with respect to the axis-normal contact faces, which gradient increases from one wave line portion φ₁ to the next φ₂ with an increasing distance from an original minimum or maximum.

With the help of the means mentioned here, the characteristic spring curve can be divided into portions of different spring rates, wherein, in adjoining portions of travel, the spring rate in the respective following portion of travel is greater than in the respective previous portion of travel, starting from the starting height h of the ondular washer or wave-shaped spring.

The heights of the individual portions of travel can substantially be freely selected by selecting the length and curvature of the individual wave line portions and thus the changing of contact points. The same applies to the respective spring rates of the individual portions of travel which, substantially depend on the degree of curvature of the curved line of the individual wave line portions.

As a result of the shape of the wave line, the force introduction points change in a defined way during the increasing rate of shortening or compression of the ondular washer or wave-shaped spring (increasing travel). From a defined compression rate onwards, in accordance with the flattening and forcing into contact of a wave line portion, the free wave line length of the ondular washer or wave-shaped spring is shortened in a defined way between the contact points (load introduction points) and, as intended, the spring rate increases step-like.

In a preferred embodiment, the individual wave line portions adjoin one another with narrow radii of transition.

As far as the total extension of the wave line is concerned, it is proposed that there are provided at least two minima and two maxima across the circumference. However, it is possible to freely select a larger number, specifically six minima and six maxima.

In a preferred embodiment the wave line extends between the minima and the maxima so as to monotonically rise or fall.

The extension of the individual wave line portions has been selected to be such that the flattening of a wave line portion and the contact between a flattened wave line portions and a contact face take place approximately simultaneously. At this point in time, the contact point of the ondular washer or wave-shaped spring changes from the original or previous contact point substantially stepwise to the end point of the wave line portion which had just been flattened. The same process is then repeated with the next wave line portion which, initially, as from the new contact point, is still curved away from the contact face. Because of the shortened length of the free wave line regions between the contact points, flattening said wave line portion required higher forces. Said effect is substantially based on the fact that the wave line portions are formed like unilaterally clamped-in, loaded bending beams which, with an increasing load, are bent to form a straight line, analogously to an increasing load removal from a bending beam which had previously been loaded by an individual load at its free end.

Ondular washers or wave-shaped springs in accordance with the invention are particularly suitable for being used as contact or damping springs for multi-plate couplings in automatic transmissions for motor vehicles. Because of the progressive characteristic spring rate, said springs do not suffer from adverse impact noise which used to occur in earlier spring types. Overall, said ondular washer or wave-shaped springs improve the comfort conditions during gear changing.

FIG. 1 shows the wave line of an inventive ondular washer or wave-shaped spring as compared to the wave line of a prior art ondular washer or wave-shaped spring according to their height coordinates and circumference coordinates.

FIG. 2 shows the characteristic spring curve of an inventive ondular washer or wave-shaped spring

-   -   a) calculated theoretically     -   b) measured on an actual part.

FIG. 3 shows an inventive wave-shaped spring in the undeformed condition

-   -   a) in a side view     -   b) in a plan view.

FIG. 4 shows an inventive ondular washer or wave-shaped spring in different shortened stages (with different lifts)

-   -   a) undeformed     -   b) with a first spring travel h ₁     -   c) with a second spring travel h₂.

FIG. 5 shows an inventive ondular washer or wave-shaped spring in a 3D illustration.

FIG. 1 shows the wave line of an inventive spring as compared to the wave line of a prior art spring with their height coordinates in a circumferential range of 360°/6 waves=60°. It can be seen that the two ondular washers or wave-shaped springs, each comprise six identical, adjoining circumferential regions over a total of 360°. The prior art ondular washer or wave-shaped spring extends in a substantially cosine way across the circumferential range illustrated, with the minima min₁ and min₂ and a maximum max₁ also being shown. The latter constitute contact points relative to contact faces which are axis-normal relative to the X-axis and which are positioned on level x=0 and x=−1. When the spring is axially shortened in the direction of the height coordinate x, said contact points remain substantially unchanged in the case of a prior art spring, with the spring rate remaining substantially constant as a function of the travel path in the direction of the X-axis.

However, in the case of a wave line of an inventive ondular washer or wave-shaped spring, the wave line is divided into different portions. The shape of the wave line in one portion corresponds to the bent line of a curved beam. Starting from the minima min₁ and min₂ as well as the maximum max₁, deformation, at a first spring rate r₁, takes place in the first wave line portions up to the points min_(1′), min_(2′), max_(1′), max_(1″). In the adjoining second wave line portions, deformation takes place at a second high spring rate r₂. The transition from one wave line portion to the next wave line portion is characterized by the the new contact points min_(1′), min_(2″), max_(1′), max_(1″) which are formed after the first wave line portions have been flattened. As a result, the circumferential distance of the contact-free wave line range between the effective contact points is shortened.

FIG. 2 shows the characteristic spring curve of an inventive ondular washer or wave-shaped spring whose curve extends in accordance with FIG. 1, with the deformation forces F being entered as a function of the height coordinate x. Starting from the wave height h, a first shorted region (travel) h₁ occurs at a lower spring rate and an adjoining second shortened region (travel) h₂ occurs at a higher spring rate. Illustration a) shows the calculated theoretical characteristic curve and illustration b) the measured characteristic curve of an actual part.

FIG. 3 shows an inventive ondular washer or wave-shaped spring, with illustration b) (plan view) showing the following parameters: D_(a) outer diameter D_(m) mean diameter D_(i) inner diameter b ring width;

and illustration a) (side view) showing the following parameters: b ring width t ring thickness l_(o) spring height h wave height.

FIG. 4 once again shows the ondular washer or wave-shaped spring according to FIG. 3 in a side view: in illustration a) in an undeformed condition, in illustration b) during deformation by the axial travel h₁ in the first region of the characteristic curve and in illustration c) during deformation by the axial travel h₁+h₂, with h₂ being positioned in the second region of the characteristic curve.

FIG. 5 shows an inventive ondular washer or wave-shaped spring with a number of n=5 wave regions in a 3D illustration. 

1. An axially acting ondular washer or wave-shaped spring consisting of a closed annular member which comprises a central x-axis and which is periodically ondulated across the circumference, wherein a wave line extends between a plurality of identical minima and identical maxima and wherein at the unloaded annular member in the minima and maxima of the wave line there are formed contact points of the annular member relative to axis-normal contact faces and between the contact points there extend contact-free wave line ranges, characterized in that, starting from each minimum and maximum, the annular member, in each circumferential direction comprises at least two wave line portions which directly adjoin one another and which, with an increasing axial load on the annular member, are individually flattened to contact the contact faces one after the other.
 2. An ondular washer or wave-shaped spring according to claim 1, characterized in that, with an increasing axial load, the contact points of the annular member relative to the contact faces discontinuously move away from the original minima and maxima.
 3. An axially acting ondular washer or wave-shaped spring consisting of a closed annular member which comprises a central x-axis and which is periodically ondulated across the circumference, wherein a wave line extends between a plurality of identical minima and identical maxima and wherein at the unloaded annular member in the minima and maxima of the wave line there are formed contact points of the annular member relative to axis-normal contact faces and between the contact points there extend contact-free wave line ranges, characterized in that, starting from each minimum and maximum, the annular member, in each circumferential direction comprises at least two wave line portions which directly adjoin one another and which correspond to the curved lines of bending beams loaded at their free ends by an individual load, wherein the curved lines of the individual wave line portions are based on individual loads which increase with an increasing distance from the original minima and maxima.
 4. An axially acting ondular washer or wave-shaped spring consisting of a closed annular member which comprises a central x-axis and which is periodically ondulated across the circumference, wherein a wave line extends between a plurality of identical minima and identical maxima and wherein at the unloaded annular member in the minima and maxima of the wave line there are formed contact points of the annular member relative to axis-normal contact faces and between the contact points there extend contact-free wave line ranges, characterized in that the annular member is so designed that a compression in direction of the x-axis under an increasing axial load there are provided at least two adjoining ranges of travel h₁, h₂, the spring rates r₁, r₂ of which are each constant, but increasing from one to the next with an increasing path of travel (r₂>r₁).
 5. An ondular washer or wave-shaped spring according to claim 4, characterized in that, at compression of the annular member in the direction of the X-axis an increasing axial load, at the transition from one range of travel h₁ to the next range of travel h₂ the contact points of the annular member relative to the contact faces discontinuously move away from the original minima and maxima.
 6. An axially acting ondular washer or wave-shaped spring consisting of a closed annular member which comprises a central x-axis and which is periodically ondulated across the circumference, wherein a wave line extends between a plurality of identical minima and identical maxima and wherein at the unloaded annular member in the minima and maxima of the wave line there are formed contact points of the annular member relative to axis-normal contact faces and between the contact points there extend contact-free wave line ranges, characterized in that, starting from each minimum and maximum, the annular member, in each circumferential direction comprises at least two wave line portion φ₁, φ₂ which directly adjoin one another and which each have a constant gradient with respect to the axis-normal contact faces, which gradient increases from one wave line portion φ₁ to the next φ₂ with an increasing distance from an original minimum or maximum.
 7. An ondular washer or wave-shaped spring according to one of claims 1 to 6, characterized in that the individual wave line portions adjoin one another with radii of transition.
 8. An ondular washer or wave-shaped spring according to any one of claims 1 to 7, characterized in that there are provided at least two minima and two maxima in the entire wave line.
 9. An ondular washer or wave-shaped spring according to claim 8, characterized in that there are provided six maxima and six minima in the entire wave line.
 10. An ondular washer or wave-shaped spring according to any one of claims 1 to 9, characterized in that the annular member comprises a constant width b and thickness t respectively across the circumference.
 11. An ondular washer or wave-shaped spring according to any one of claims 1 to 9, characterized in that, on its outside and/or its inside, the annular member comprises a toothing constituting anti-rotation means.
 12. An ondular washer or wave-shaped spring according to one of claims 1 to 11, characterized in that the wave line extends so as to monotonically rise or fall between the minima and the maxima. 